1. Field of the Invention
The present invention pertains to a high efficiency furnace and a low profile furnace that each comprise a compact enclosure for residential use and an air distribution blower housing that is designed with an outer wall having an exponentially increasing expansion angle and an enlarged air outlet opening. The enlarged outlet opening slows down and spreads out the air flow from the blower housing over a greater area of the secondary heat exchanger and the primary heat exchanger of the high efficiency furnace, and over a greater area of the heat exchanger of a low profile furnace. Thus, the blower housing enables less air pressure drop through the heat exchangers, which increases the efficiency of the blower operation. The design of the blower housing also efficiently turns the velocity head of the air flow to usable static pressure at the housing air outlet. The enlarged air outlet opening of the blower housing is achieved without increasing the exterior dimensions of the blower housing whereby the blower housing is used in a compact enclosure for residential use. This is accomplished by utilizing a unique design volute outer wall of the blower housing that has a unique exponentially increasing expansion angle in the direction of air flow through the blower housing and compact relative positioning of the blower housing and heat exchangers in the furnace enclosure.
2. Description of Related Art
High efficiency residential natural gas powered furnaces are becoming more and more common. A furnace of this type is defined in the industry as a 90+ AFUE (Annul Fuel Utilization Efficiency) furnace. A 90+ furnace converts more than 90% of the fuel supplied to the furnace to heat, with the remainder being lost through the chimney or exhaust flue. These particular types of furnaces employ a primary heat exchanger found in most any type of furnace, plus an additional secondary heat exchanger. The secondary heat exchanger increases the capacity of the furnace to convert the heat of the gas combustion to the distribution air flow from the furnace, and thereby defines the furnace as a high efficiency furnace.
The typical construction of a high efficiency furnace 10 is shown in FIG. 1. The furnace 10 has an external housing enclosure 12 with an interior volume 14. Several portions of the side walls of the furnace enclosure 12 shown in FIG. 1 have been removed to illustrate the interior components of the furnace. The dimensions of the furnace enclosure 12 are determined to contain all of the component parts of the furnace in the enclosure 12, without the enclosure occupying a significant area in the residence in which the furnace is installed. In contrast, commercial furnaces are typically mounted on the roof of a building or at some other location outside the building where there are no size restraints. Because commercial furnaces with their large capacity are located outside the structures they serve, there is no need to position the component parts of the furnace relative to each other to minimize the size of the furnace enclosure as there is in residential furnaces.
An air inlet opening is typically provided in a side wall or in the bottom of the furnace enclosure. The air inlet opening can be covered by an air filter that allows ambient air in the environment surrounding the enclosure 12 to easily pass through the opening and enter the enclosure interior 14. Alternatively and more frequently, the air inlet opening of the furnace enclosure communicates with a cold air return duct system of the residence. The cold air return duct system channels ambient air from throughout the residence to the furnace enclosure.
The furnace enclosure also has an air distribution outlet opening 18. The outlet opening communicates with an air distribution conduit or duct system of the residence in which the furnace is installed. In FIG. 1, the air distribution outlet opening is located at the top of the enclosure 12. The air heated by the high efficiency furnace 10 is discharged to the air distribution conduit system (not shown) through the distribution air outlet opening 18.
In the typical construction of a high efficiency furnace represented in FIG. 1, a primary heat exchanger 22 is located at the top of the enclosure 12 adjacent the distribution air outlet opening 18. A secondary heat exchanger 24 that qualifies the furnace as a high efficiency furnace is located directly below the primary heat exchanger 22.
An air distribution blower 26 that draws ambient air into the furnace enclosure 12 is positioned just below the secondary heat exchanger 24. A motor (not shown) of the blower rotates a fan wheel 28 in the interior of the blower in a clockwise direction as viewed in FIG. 1. This rotation of the fan wheel 28 draws the ambient air into the blower 26 as represented by the arrow labeled (AIR FLOW) in FIG. 1, and pushes the ambient air out of the blower through the secondary heat exchanger 24, then through the primary heat exchanger 22, and then out of the enclosure through the air distribution outlet opening 18.
A typical blower 26 includes a blower housing that contains the fan wheel 28. The typical blower housing includes an exterior or outer wall 32 having a scroll or volute configuration. The outer wall 32 spirals around the fan wheel 28 in the direction of fan wheel rotation. A pair of side walls, only one of which is shown in FIG. 1, cover over opposite sides of the volute outer wall 32 and enclose the interior of the blower 26.
As shown in FIG. 1, the typical volute outer wall 32 of the blower housing has a constant expansion angle as it extends in the fan wheel rotation direction around the fan wheel. What is meant by expansion angle is the angle at which the outer wall expands in the direction of fan wheel rotation from any point on the exterior of the outer wall 32. In the typical construction of a blower housing outer wall 32 such as that shown in FIG. 1, this expansion angle is constant for all points along the volute outer wall 32 in the rotation direction, resulting in a gradually increasing distance between the outer circumference of the fan wheel 28 and the outer wall 32 as the outer wall extends in the rotation direction around the fan wheel.
The air distribution blower 26 of the typical high efficiency furnace represented in FIG. 1 has been found to be disadvantaged in that the flow of air directed from the blower is primarily concentrated on only small portions of the secondary heat exchanger 24 and the primary heat exchanger 22. The air flow directed from the blower through the portions of the heat exchangers is represented by the arrows 34 shown in FIG. 1. As seen in FIG. 1, the scroll configuration of the volute outer wall 32 and the close positioning of the fan wheel 28 to the interior surface of the outer wall 32 primarily concentrates the flow of air through the reduced areas of the secondary heat exchanger 24 and the primary heat exchanger 22 shown to the left in FIG. 1. This reduces the efficiency of heat transfer from the heat exchangers to the air flow. The concentration of the air flow to reduced areas of the secondary 24 and the primary 22 heat exchanger also results in a significant pressure drop. This additional pressure drop requires additional blower horsepower, i.e. a larger blower motor. The requirement for a larger blower motor decreases the electrical efficiency of the furnace. Also, the heat generated by operating a larger motor would especially detract from the cooling system efficiency when an air conditioning heat exchanger is added at the air outlet opening 18 in the enclosure 12. If the problem of the concentration of air flow through the reduced areas of the heat exchangers is attempted to be overcome by simply enlarging the size of the exhaust outlet of the conventional blower housing, the resulting scroll shape of the blower housing would not be able to adequately convert the velocity head of the air flow through the housing into static pressure of the resulting blower system and the overall blower system would not be successful in saving energy.